Previously a capsule is widely used in the field of drugs, cosmetics, health foods, etc. (Patent Literature 1). Recently because of the spread of its usage, the technology of the capsule to be rupturable as well as the technology of the capsule not to be rupturable by increasing the capsule shell strength has been required.
The usage of the technology of the capsule to be rupturable includes, for example, that at the time of smoking, a smoker enjoys a fragrance by rupturing the capsule containing perfume, etc. wherein the capsule is buried in the cigarette filter, and a smoker enjoys also the sound and feeling at the time of rupturing the capsule.
Therefore, in order to make capsule rupturable, the capsule with a thin capsule shell has been developed. For example, the Patent Literature 2 discloses, when the soft capsule has the joint, to slant the adhesion surface of the joint and to increase the thickness of only the bonding portion with a fringe provided by a special mold. The Patent Literature 2 discloses to suppress the adhesive shell portion to be locally thin in a soft capsule which has the joint for a bathing additive.
However, when the capsule shell is thicken, the capsule strength becomes higher and the capsule cannot be crushed by the fingers, but the capsule is deformed without rupturing.
When increasing the content of the gelling agent in the capsule shell in order to avoid the problem, manufacturing the capsule may become difficult due to the high viscosity.
In addition, the perfume contained in the capsule is often volatile and therefore, it requires storage stability of the content until the time used. Furthermore, when the capsule is used in a smoking device, the capsule may be soften by moisture during smoking, and even if a smoker imposes a pressure by the fingers, there is a risk that a capsule might not be ruptured.
It is well known to use, for example, carrageenan as a gelling agent of the capsule shell. However, as carrageenan has a high viscosity-increasing effect and has a fast gelling speed, to contain a large amount of carrageenan in the capsule shell disturbs the encapsulation. In other words, if the content ratio of carrageenan is high, the capsule has poor moldability such as poor sphericity and the ease of coagulation at the injection nozzle tip because of the high viscosity and the early gelation, which made it impossible to prepare the preferable capsule.
On the other hand, for example, the Patent Literature 3 discloses that blending carrageenan with starch, dextrin and non-gelling polysaccharides as a material or filler to increase the solid concentration of the shell achieves the low viscosity and the relaxation of the gelation velocity.
However, not only in the case employing the gelatin as a shell but also in the case employing carrageenan which is regarded as lower hygroscopicity comparing with gelatin, when blending starch, dextrin, non-gelling polysaccharides, as the shell is subject to the effect of humidity, in some cases it is hard to get added value over time stably such as easiness of rupturing by the fingers after drying, the sound and feeling at the time of rupturing the capsule.
Also, the Patent Literatures 4 to 11 disclose burying the capsule in the cigarette filter, but it has not been taken into consideration that added value such as production of the capsule, storage stability, easiness of rupturing by the fingers after drying, and the sound and feeling at the time of rupturing the capsule.
Furthermore, when the breakable capsule is used in cigarettes, as cigarettes are used in local climate of a wide variety worldwide, there is room for improving heat resistance and moisture resistance.